1. Field of the Invention
The present invention relates to a laminate with a peelable top layer, which can be used as building materials that survive severe use conditions for an extended time, and be easily recycled after use, and a method of peeling off the top layer from the laminate for the recycling.
2. Disclosure of the Prior Art
In the past, laminated boards have been widely used in many application fields, for example, as building materials for office, condominium and house, materials for interior decoration, and car interiors. The laminated boards are usually produced by bonding a substrate such as a wooden board or a plasterboard with a decorated plastic sheet, for example, a polyvinyl chloride, polyester or polyolefin sheet having a printed pattern such as grain of wood, or a decorated metal plate, for example, a paint coated metal plate, steel plate having an anti-corrosive surface obtained by a phosphate treatment, or an aluminum plate with an anodic oxidation coating.
However, when performing repair or demolition in the above-described applications, it is desired to peel off the metal or plastic sheet from the laminated board. If the metal or plastic sheet cannot be easily peeled off, all of the laminated board must be disposed as industrial waste. In recent years, the influence that the industrial waste gives to environment becomes an object of public concern. Therefore, it is tried to improve easiness of peeling the metal or plastic sheet, and the easiness of recycling or reusing the laminated board after use.
For example, Japanese Patent Early Publication [KOKAI] No. 56-61468 discloses a peelable adhesive, which is characterized by containing 30 to 100 parts by weight of microspheres having the capability of volume expansion by heating with respect to 100 parts by weight of an adhesive component. By use of this adhesive, there are advantages that an operation of peeling labels from labeled bottles after use or of tearing off an unnecessary seal from a purchased article becomes easy.
However, in the building-materials field, a very high bonding strength between the metal or plastic sheet and the substrate is needed, as compared with the above-described cases. In particular, when producing the laminated board with use of a specific plastic sheet such as polyester or polyolefin that has the difficulty to adhesion, it is necessary for the laminated board to demonstrate excellent performance in water resistance, heat resistance, heat creep resistance, and resistance to hot water, in addition to the high bonding strength.
In these circumstances, it is waited to develop a laminated board having improved easiness of peeling the plastic sheet or the metal plate, i.e., the easiness of recycling or reusing the laminated board after use, while providing excellent bonding performance of the laminated board that can survive severe use conditions for an extended time.